听力原文：The story of silk is a fascinating one. About 4,000 years ago the Chinese discove

听力原文： The story of silk is a fascinating one. About 4,000 years ago the Chinese discovered the secret of the cocoon. No one knows exactly how or when this was made. One story says that a young princess was drinking tea in her garden and watching the silkworm spin cocoon. By chance one dropped into her tea, and the hot liquid softened it. When the girl tried to take the cocoon out of her tea. She pulled out a long silk thread.

The Chinese learned to weave the silk thread into cloth. For 2,000 years they were the only people who knew how to make silk. The Chinese merchants sold silk cloth throughout Asia and Europe and became rich. Silk was so expensive that it was called "the cloth of the Kings". Everyone wanted to learn how to make silk, but the Chinese kept the secret carefully guarded. Finally the secret was stolen. In the sixth century, two monks learned about the silk worms and their cocoons. They spent several years in China and finally found a way to take some worm eggs out of the country. The monks also carried bamboo canes. One day they hid some eggs in the hollow canes, and walked out of China with them. It is said that the development of the silk industry in other countries came from those few eggs which the monks had carried out of China.

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A．The silk covering made by an insect.

B．The silk covering made by a silkworm.

C．The soft protective covering made by an animal.

D．The hard protective covering made by an animal.